The patch titled Subject: padata: Fix possible divide-by-0 panic in padata_mt_helper() has been added to the -mm mm-hotfixes-unstable branch. Its filename is padata-fix-possible-divide-by-0-panic-in-padata_mt_helper.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Waiman Long longman@redhat.com Subject: padata: Fix possible divide-by-0 panic in padata_mt_helper() Date: Tue, 6 Aug 2024 13:46:47 -0400

We are hit with a not easily reproducible divide-by-0 panic in padata.c at bootup time.

[ 10.017908] Oops: divide error: 0000 1 PREEMPT SMP NOPTI [ 10.017908] CPU: 26 PID: 2627 Comm: kworker/u1666:1 Not tainted 6.10.0-15.el10.x86_64 #1 [ 10.017908] Hardware name: Lenovo ThinkSystem SR950 [7X12CTO1WW]/[7X12CTO1WW], BIOS [PSE140J-2.30] 07/20/2021 [ 10.017908] Workqueue: events_unbound padata_mt_helper [ 10.017908] RIP: 0010:padata_mt_helper+0x39/0xb0 : [ 10.017963] Call Trace: [ 10.017968] <TASK> [ 10.018004] ? padata_mt_helper+0x39/0xb0 [ 10.018084] process_one_work+0x174/0x330 [ 10.018093] worker_thread+0x266/0x3a0 [ 10.018111] kthread+0xcf/0x100 [ 10.018124] ret_from_fork+0x31/0x50 [ 10.018138] ret_from_fork_asm+0x1a/0x30 [ 10.018147] </TASK>

Looking at the padata_mt_helper() function, the only way a divide-by-0 panic can happen is when ps->chunk_size is 0. The way that chunk_size is initialized in padata_do_multithreaded(), chunk_size can be 0 when the min_chunk in the passed-in padata_mt_job structure is 0.

Fix this divide-by-0 panic by making sure that chunk_size will be at least 1 no matter what the input parameters are.

Link: https://lkml.kernel.org/r/20240806174647.1050398-1-longman@redhat.com Fixes: 004ed42638f4 ("padata: add basic support for multithreaded jobs") Signed-off-by: Waiman Long longman@redhat.com Cc: Daniel Jordan daniel.m.jordan@oracle.com Cc: Steffen Klassert steffen.klassert@secunet.com Cc: Waiman Long longman@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/padata.c | 7 +++++++ 1 file changed, 7 insertions(+)

--- a/kernel/padata.c~padata-fix-possible-divide-by-0-panic-in-padata_mt_helper +++ a/kernel/padata.c @@ -517,6 +517,13 @@ void __init padata_do_multithreaded(stru ps.chunk_size = max(ps.chunk_size, job->min_chunk); ps.chunk_size = roundup(ps.chunk_size, job->align);

+ /* + * chunk_size can be 0 if the caller sets min_chunk to 0. So force it + * to at least 1 to prevent divide-by-0 panic in padata_mt_helper().` + */ + if (!ps.chunk_size) + ps.chunk_size = 1U; + list_for_each_entry(pw, &works, pw_list) if (job->numa_aware) { int old_node = atomic_read(&last_used_nid); _

Patches currently in -mm which might be from longman@redhat.com are

padata-fix-possible-divide-by-0-panic-in-padata_mt_helper.patch watchdog-handle-the-enodev-failure-case-of-lockup_detector_delay_init-separately.patch